Fluid responsive flow switch



L. J. KMIECIK FLUID RESPONSIVE FLOW SWITCH Sept. 26, 1967 'Filed May 13,1965 2 Sheets-Sheet 1 Sept. 26, 1967 L.. .1.l KMIECIK FLUID RESPONSIVEFLOW SWITCH 2 Sheets-Sheet 2 Filed Ma 13, 1965 y N www: l

um QN/ uw @@MH fnl/eww eajaa JA United States Patent C 3,344,247 FLUIDRESPUNSIVE FLOW SWITCH Leopold J. Kmiecik, Lincolnwood, Ill., assignerto McDonnell & Miller, Inc., Chicago, Ill., a corporation of DelawareFiled May 13, 1965, Ser. No. 455,498 11 Claims. (Cl. 20u-81.9)

The present invention relates to fluid flow switches and moreparticularly to switches responsive to ilow of fluid such as air in anair duct.

It is desirable in systems embodying air conducting ducts to provide owswitches sensitive to the flow or lack of ow of air in the air ducts, inwhich said flow switches may be associated with suitable electricalcircuits embodying signalling devices located, for example, .at acontrol panel with energization of such signalling devices beingcontrolled in response to opening and closing of the flow switches.

The flow switch of the present invention has particular utility for usewith air ducts for sensing iiow of air therein. In most air conductingsystems, the air ow will frequently pulsate which, with conventionalknown air flow switches will cause undesirable opening and closing orfluttering of the switches.

Accordingly, it is an object of the present invention to provide an airflow switch which will not open and close over a predetermined range ofpulsating of fluid in a Huid conducting duct.

Also, known air flow switches embody a paddle or vane for positioning inan air duct and which paddle or vane effects opening or closing of anassociated switch by movement or lack of movement of air in the airduct. In such known systems and especially at high velocity of air flowin an air duct, the paddles or vanes offer substantial resistance to airflow and impede the eiciency of movement of air through an air duct, andadditionally, cause iiuttering or undesirable off and on actuation ofswitch means of such known air switches.

It is a further object ofthe present invention to provide an air owswitch embodying novel paddle meansrthe effective cross-sectional areaof which lessens, especially at high velocity air flows, through an airduct so as to not impede or unduly restrict air iiow through the duct,and additionally, to prevent erratic operation of switch means of theair flow switch.

A further object of the present invention is to provide an airflowswitch having pivoted paddle rod means supported and being movable aboutits pivot by movement of the aforementioned paddle means to controloperation of switch means of the air flow switch.

A further object is to provide an air ow switch as last noted embodyingpaddle rod spring means associated with the aforementioned paddle rodmeans to yieldingly resist movement of the paddle means in the directionthereof caused by air flow in an air duct.

A further object is to provide an air flow switch as last notedembodying paddle rod stop means for preventing pivotal movement of thepaddle rod means beyond a predetermined end position in the directionthereof caused by -air ow in an air duct.

A further object of the invention is to provide an air ow switchembodying switch means adapted to be actuated by movement of the paddlerod means before the latter is disposed in its aforementionedpredetermined end position so as to prevent fluttering of the switchmeans by pulsing of air in an air duct with which the air ow switch isassociated.

A further object is to provide an air How switch having novel sealingmeans for preventing air in the duct from entering the air ow switchhousing.

Patented Sept. 26, 1967 ICC The above and other objects and advantagesof my invention will appear from the following detailed description of apreferred embodiment of the invention.

Now in order to acquaint those skilled in the art with the manner ofconstructing and utilizing an air ow switch in accordance with theprinciples of the present invention, there is described below inconnection with the accompanying drawings, a preferred embodiment of theinvention.

In the drawings:

FIGURE 1 is a vertical cross-sectional view of an air flow switch of thepresent invention shown mounted on the side wall of an air duct with theview being taken substantially along the line 1-1 of FIGURE 2 looking inthe direction indicated by the arrows, and with certain parts shown inelevation. l

FIGURE 2 is a horizontal cross-sectional view of the air flow switch andduct of FIGURE 1 with certain parts shown in elevation;

FIGURE 3 is a detail vertical cross-sectional view taken substantiallyalong the line 3 3 of FIGURE 1 looking in the direction indicated by thearrows;

FIGURE 4 is a detail Vertical cross-sectional view taken substantiallyalong the line 4-4 of FIGURE 1 looking in the direction indicated by thearrows;

FIGURE 5 is a plan View of the paddle rod means and air sealing meansembodied in the air flow switch of FIG- URES 1 and 2;

FIGURE 6 is a detail vertical sectional view taken substantially alongthe line 6-6 of FIGURE 1 looking in the direction indicated by thearrows showing the paddle means of the air flow switch of FIGURES 1 and2 in normal position and in absence of air flow in the air duct;

FIGURE 7 is a view corresponding to FIGURE 6 showing the paddle means inone position as caused by predetermined flow of air in the air duct;

FIGURE 8 is a detail vertical sectional view taken substantially alongthe line 8-8 of FIGURE 1 looking in the direction indicated by thearrows; and

FIGURE 9 is a detail vertical sectional View taken substantially alongthe line 9--9 of FIGURE l looking in the direction indicated by thearrows.

Referring now to FIGURES 1 and 2 of the drawings there is shown an airflow switch 10 of the present invention which typically may be mountedon one vertical side wall 11 of a conventional air duct 12. The air Howswitch 10 comprises an enclosing housing, indicated generally at 13,from which paddle rod means 14 extends through the side wall 11 of andfor supporting paddle means 15 within the duct 12.

The housing 13 comprises a base mounting plate 16 providing for thesupport of air flow switch 10 at opening 17 in the side wall 11 of theduct as by securing of the peripheral flange 18 of the supporting baseplate in any suitable manner adjacent the outer surface of the wall 11around opening 17. If desired, a gasket 19 may be interposed between theinner surface of the flange 18 and the adjacent outer surface of Wall11. Flanges 20 and 21 at the base end of housing 13 are secured betweenthe supporting base 16 and a fulcrum plate member 22 by a plurality ofnuts and bolts 23, A sealing ring retainer 24 is secured to base 16 asby staking as indicated at 25. An annual sealing ring 26 preferably ofmaterial of low frictional characteristics, such as nylon or Teflon, isclamped about its periphery between sealing ring 26 and the opposedsurface of supporting base 16.

The paddle rod means 14 comprises a rod 30 at the inner end thereofwithin housing 13 through which a pivot pin 32 extends with the oppositeends of the pivot pin projecting through ears 33 of a switch actuator 34and through spaced apart ears 35 of fulcrum plate member 22.

Cotter pins 36 may be provided at opposite ends of the pivot pin 32 toretain the latter in position. The outer end of rod 30 is formed with aprojection 38 fitting or keyed in the conformably shaped opening 39 ofswitch actuator 34. A seal member 42 having a seat 43 conforming to aportion of a surface of a sphere is mounted on rod 30 with the seat 43in sliding sealing engagement with the inner edge of annular sealingring 26. A sleeve 45, paddle stop means indicated at 47, and a paddleextension rod 48 are secured to rod 3ft by a pair of pins 49 passingthrough these several components. The vsleeve 45 thus securely holds theseal member 42 in position against shoulder 52 of rod 30.

The paddle means 15, as shown, comprises a pair of components, such aspivotable paddle component means 60 and 62 mounted on paddle extensionrod 48 to extend transversely of duct 12 and in the path of air flowingthroughthe duct. The paddle component 60 is preferably fabricated oflight gauge sheet metal, and is formed with a pair of integral andspaced apart tubular bearing portions 63 along the lower edge thereofthrough which extension rod 48 extends. The paddle component 62 is ofthe same construction as paddle component 60 but is arranged with itstubular bearing portions 63 along the upper edge thereof with suchtubular bearing portions 63 of the pair of paddle components inalternate relation alongextension rod 48. Cut outs 64 and 65 are formedin paddle components 60 and 62 to provide for the reception of a washer66 adjacent the outer end of rod 48 which together with cotter pin 67retain the paddle .components 60 and 62 on the rod 48. Paddle springmeans 68 in part surrounds rod 48 substantially mid-way between oppositeends of the paddle components 60 and 62, and legs 69 and 70 of springmeans 68 engage the surfaces of the paddle components 60 and 62,respectively. The

Vaforementioned paddle stop means 47, as best seen in FIGURES 5, 6 and7, comprises a U-shaped end portion 71, the upper and lower legs 72 and73 of which are formed with slots 74 and 75, the inner ends of whichprovide stops 76 and 77, respectively, for limiting clockwise movementof pivotable paddle component 60 and counter clockwise movement ofpivotable paddle component 62 as viewed in FIGURES 6 and 7. The legs 69and 70 of the aforementioned paddle spring means 68 provide for normallydisposing the pivotable paddle components 60 and 62 to the positionsshown in FIGURE 6. In this position, the paddle components 60 and 62provide the maximum effective area of paddle means traversing the duct12 and opposing air owing through the duct in the direction of air flowas indicated by the arrow in FIGURE 2. As will be described later indetail, the spring means 68 may be selected to provide any desiredloading of the paddle components 60 and 62 and the force of such springmay be overcome by a given predetermined air flow through the duct inthe indicated direction so as to effect relative pivotal movement of thepaddle components 60 and 62 toward each other and reduce the effectivesurface area of paddle means 15 and thus provide minimum obstruction toair flow through ,the duct 12.

Referring to the aforementioned switch actuator 34, it will be seen thatit further compirses a flange 75 which has mounted thereon one end of aspring guide member 76 which at its other end provides a seat for paddlerod spring means in the form of a coil spring 77. The other end of coilspring 77 supports a spring seat member 78 and into which a bolt 79threaded in flange 80 of a switch supporting plate 82 is seated. Thebolt 79 provides for adjusting the force of the paddle rod spring means77. The switch supporting plate 82 extends transversely of and issuitably mounted in fixed relation in housing 13. The switch supportingplate 82 has a switch actuator stop member 85 secured thereto which isformed with a stop projection 86 for engaging and preventing movement ofswitch actuator 34 in a clockwise direction around the axis of pivot pin32 as viewed in FIGURE 2. A switch adjusting plate 90 carrying knownswitch means, as indicated at 92, which switch means may, for example,comprise a conventional snap action switch is mounted on switchsupporting plate 82. Suitable conventional adjusting and mounting screwmeans 91 may be provided for adjusting the plate 90 and switch meanscarried thereby to provide for the desired positioning of switchactuating blade 93 as desired. The switch actuator 34 as best seen inFIGURES l and 2 further comprises a plate member 94 for engaging theabutment 95 of switch blade 93 of the switch means 92 for effectingactuation of the latter. As noted, the switch means 92 is conventionaland may be adjusted according to conventional practice of the art andfurther may also be enclosed in a suitable protected housing asindicated at 97.

In the arrangement of components as above described, and with apredetermined air flow through the duct 12 in the direction indica-tedby the arrow in FIGURE 2, it will be observed that such air flow in theduct 12 will effect movement of paddle means 15 and control rod means 14in a clockwise direction relative to pivot pin 32, as viewed in FIGURE2, effecting movement of switch actuator 34 in a direction for engagingplate 94 thereof with the projection 9S o-f the switch blade 93 ofswitch means 92. Actuation of the switch means 92 may as previouslyindicated provide for the energization of signal means at a controlcenter indicating flow of air through the duct 12. As above mentionedthe paddle spring means 68 normally disposes the pivotable paddlecomponents 60 and 62 in position of maximum effective area against airflow through the duct, but such spring means may be selected so that ata predetermined air flow through the duct the'paddle components 69 and62 pivot toward each other and `against the force of the spring means 68to substantially lessen or render completely ineffective, the effectiveVarea of paddle means 15 restricting air flow through the duct to thusprovide for the efficient movement of air in the duct. By reason of themode of operation as last described, pulsing of air in the duct 12 inview of the small area of the paddle rod 'means and paddle `components60 and 62 in the duct serve to prevent on and off actuation of theswitch means Further, it will be observed upon predetermined air flowthrough the duct 12 as above described that the clockwise rotation ofcontrol rod means 14 as seen in FIGURE 2 about the pivot pin 32 isyieldingly resisted by compression of paddle rod spring means 77 beforemovement of switch actuator 34 is arrested by engaging the abutment 86of the paddle rod stop member'85. It is also an important `aspect of theinstant invention to provide upon movement of the paddle rod means 14 inthe manner described that the actuator member 34 effects tripping ofswitch means 92 before the actuator member 34 abuts the stop 86 so thatpulsing of air flow in the duct 12 will not effect off `and on actuationof switch meansV 92. The paddle rod stop member may thus be positionedto provide for the desired further movement of the paddle rod means 14and paddle components 60and 62 in a clockwise direction as viewed inFIGURE 2 such that predetermined movement of such components in acounterclockwise direction about the pivot pin 32 as may be caused bypulsing of air in duct 12 will not effect off and on tripping of theswitch means 92 by the switch actuator 34. Thus, theV switch means 92may be closed prior to movement of the switch actuator 34 being arrestedby the stop member 85 to thus avoid bouncing or opening and closing ofswitch 92 due to irregular or pulsing air flow in the duct 12. Y

In the aforementioned pivotal movement of the control rod means 14 itwill be observed that the spherical sealing surface 43 of the seal 42maintains sealing engagement with the annular sealing ring 24 forpreventing air in the duct from escaping into the housing 13 of the airflow switch means 10.

While there has been shown and described a preferred embodiment of theair flow switch of the present invention, it will be understood thatvarious modifications and rearrangements may be made therein withoutdeparting from the spirit and scope of the invention.

I claim:

1. A flow switch for association with a fluid conducting duct comprisinga housing adapted to be mounted on said duct, electrical switch meansmounted in said housing, paddle rod means pivotally mounted at one endthereof within said housing and with the other end of said paddle rodmeans extending into said duct, paddle means carried at said other endof said paddle rod means, said paddle means being movable by fluid flowin said duct to effect movement of said paddle rod means, said paddlemeans including pivotable paddle components movable around said otherend of said paddle rod means and relative to each other from a firstposition by predetermined flow of air through said duct for decreasingthe effective surface area of said paddle components of said paddlemeans exposed to fluid flow in said duct, spring means in engagementwith said pivotable paddle components for normally biasing said paddlecomponents towards said first position, and switch actuator meansbetween said one end of said paddle rod means and said electrical switchmeans for opening and closing the latter upon predetermined movement ofsaid paddle rod means.

2. A flow switch for association with a fluid conducting duct comprisinga housing adapted to be mounted on said duct, electrical switch meansmounted in said housing, paddle rod means pivotally mounted at one endthereof in said housing and with the other end of said paddle rod meansextending into said duct, paddle means carried at said other end of saidpaddle rod means, said paddle means being movable by fluid flow in saidduct to effect pivotal movement or" said paddle rod means, said paddlemeans comprising pivotable paddle components movable around said otherend of said paddle rod means and relative to each other from a firstposition by predetermined flow of fluid through said duct for decreasingthe effective surface area of said paddle components of said paddlemeans exposed to fluid flowing in said duct, spring means in engagementsaid pivotable paddle components for normally biasing said paddlecomponents toward said first position, and i switch Iactuator meansbetween said one end of said paddle rod means and said electrical switchmeans for opening and closing the latter upon predetermined pivotalmovement of said paddle rod means.

3. A flow switch for association with a fluid conducting duct comprisinga housing adapted to be mounted on said duct, electrical switch vmeansmounted in said housing, paddle rod means pivotally mounted in saidhousing, paddle means adapted to beY disposed in said duct carried bysaid paddle rod means, spring means connected to said paddle rod meansVfor resisting movement of said paddle rod means, said paddle means beingmovable by fluid flow in said ductito effect pivotal movement of saidpaddle rod meansl against said spring means, said paddle meanscomprising pivotable paddle components movable relative to each otherfrom a first p-osition by predetermined flow of air through said ductfor decreasing the effective surface area of said paddle components ofsaid paddle means exposed to fluid flowing in said duct, spring means.between said paddle :rod means and said pivotable paddle componentsnormally biasing said paddle components toward said first position, andswitch actuator means between said paddle rod means and said electricalswitch means for opening and closing the latter upon predeterminedpivotal movement of said paddle rod means.

4. A flow switch for association with a fluid conducting duct comprisinga housing adapted to be mounted on said duct, electrical switch meansmounted in said housing, paddle rod means pivotally mounted in saidhousing, paddle means adapted to be disposed in said duct carried bysaid paddle rod means, spring means connected to said paddle rod meansfor resisting movement of said paddle rod means, means in engagementwith said spring means for adjusting the resistance of the latter, saidpaddle means being movable by fluid flow in said duct to effect pivotalmovement of said paddle rod means against said spring means, said paddlemeans comprising pivotable paddle components movable relative to eachother from a first position by predetermined flow of air through saidduct for decreasing the effective surface area of said paddle componentsof said paddle means exposed to fluid flowing in said duct, spring meansbetween said paddle rod means and said pivotable paddle componentsnormally biasing said paddle components toward said first position, andswitch actuator means between said paddle rod means and said electricalswitch means for opening and closing the latter upon predeterminedpivotal movement of said paddle rod means.

5. A flow switch for association with a fluid conducting duct comprisinga housing adapted to be mounted on said duct, electrical switch meansmounted in said housing, paddle rod means pivotally mounted in saidhousing, paddle means adapted to be disposed in said duct carried bysaid paddle rod means, said paddle means being mov able by engagementtherewith of fluid flowing in said duct to effect pivotal movement ofsaid paddle rod means, paddle rod stop means mounted in said housing forlimiting movement of said paddle rod means by fluid flow in said ductagainst said paddle means, paddle rod spring means connected to saidpaddle rod means for resisting movement of said paddle rod means beforeengagement I of the latter with said paddle rod stop means, said paddlemeans comprising pivotable paddle components movable relative to eachother from a first position bypredetermined flow of fluid through saidduct for decreasing the effective surface area of said paddle componentsof said paddle means exposed to fluid flowing in said duct, spring meansbetween said paddle rod means and said pivotable paddle componentsnormally biasing said paddle components toward said first position, andswitch actuator means between said paddle rod means and said electricalswitch means for opening and closing the latter upon predeterminedpivotal movement of said paddle rod means.`

6. A flow switch for association with a fluid conducting duct comprisinga housing adapted to be mounted on said duct, electrical switch meansmounted in said housing, said electrical switch means comprising amovable switch member, paddle rod means pivotally mounted in saidhousing, paddle means adapted to be disposed in said duct carried bysaid paddle rod means, said paddle means being movable in one directionby engagement therewith of fluid flowing in said duct to effect pivotalmovement in one direction of said paddle rod means, paddle rod stopmeans mounted in said housing for limiting movement of said paddle rodmeans in said one direction of movement thereof, paddle rod spring meansconnected to said paddle rod means for resisting movement of said paddlerod means in said one direction of movement thereof before engagement ofthe latter with said paddle rod stop means,

said paddle means comprising pivotable paddle compo# nents movablerelative to each other from a first position by predetermined flow offluid through said duct for decreasing the effective surface area ofsaid paddle components of said paddle means exposed to fluid flow insaid duct, spring means between said paddle rod means and said pivotablepaddle components normally biasing said paddle components toward saidrst position, and switch actuator means between said paddle rod meansand said switch member of said electrical switch means for opening andclosing the latter upon predetermined pivotal movement of said paddlerod means in said one direction and before engagement of said paddle rodmeans with said stop means.

7. A tiow switch for association with an air conducting duct comprisinga housing adapted to be mounted on said duct, electrical switch meansmounted in said housing, paddle rod means pivotally mounted adjacent oneend thereof in said housing and having an outwardly projecting portionextending through an opening in said housing for positioning in said airduct, paddle means adapted to be disposed in said air duct carried bysaid outwardly projecting portion of said paddle rod means, an annularsealing ring mounted at said opening of said housing, a seal membermounted on said paddle rod means, said seal member having a surfaceconforming to a portion of the surface of a sphere engaging said sealingring for preventing entry of air into said housing from said duct, saidpaddle means being movable by air ow in said air duct to effect pivotalmovement of said paddle rod means, said paddle means comprisingpivotable paddle components movable relative to each other by liow ofair through said duct for decreasing the effective surface area of saidpaddle components of said paddle means exposed to air ow in said duct,and switch actuator means between said paddle rod means and saidelectrical switch means for opening and closing the latter uponpredetermined pivotal movement of said paddle rod means.

8. A flow switch for association with an air conducting duct comprisinga housing adapted to be mounted on said duct, electrical switch meansmounted in said housing, paddle rod means pivotally mounted adjacent oneend thereof in said housing and having an outwardly projecting portionextending through an opening in said housing for positioning in said airduct, paddle means adapted to be disposed in said air duct carried bysaid outwardly projecting portion of said paddle rod means, said paddlemeans being movable by air flow in said air duct to effect pivotalmovement of said paddle rod means, said paddle means comprisingpivotable paddle components normally disposed in a first positionpresenting a predetermined surface area exposed to air owing in saidduct, spring means between said paddle rod means and said paddle meansnormally biasing said paddle components toward said rst position, andsaid paddle components being movable toward each other by predeterminedflow of air through said duct for decreasing the effective surface areaof said paddle components of said paddle means exposed to air ow in saidduct, and switch actuator means between said paddlerod means and saidelectrical switch means for opening and closing the latter uponpredetermined pivotal movement of said paddle rod means.

9. A ow switch for association with an air conducting duct comprising ahousing adapted to be mounted on said duct, electrical switch meansmounted in said housing, paddle rod means pivotally mounted adjacent oneend thereof in said housing and having an outwardly projectlng portionextending through an opening in said housing for positioning in said airduct, paddle means adapted to be disposed in said air duct carried bysaid outwardly projecting portion `of said paddle rod means, said paddlemeans being movable by air flow in said air duct to effect pivotalmovement of said paddle rod means, paddle stop means carried by saidpaddle rod means, said paddle meanscomprising pivotable paddlecomponents movable relative to each other, spring means carried by saidpaddle rod means for engaging said paddle means for biasing said paddlecomponents toward said paddle stop means for disposing said paddle meansin a first position presenting a predetermined surface area exposed toair flowing in said duct, said paddle components being movable towardeach other against the force of said spring means by predetermined ow offluid through said duct for decreasing the effective surface area ofsaid paddle components of said paddle means exposed to air flow in saidduct, and switch actuator means between said paddle rod means and saidelectrical switch means for opening and closing the latter uponpredetermined pivotal movement of said paddle rod means.

10. A ow switch for association with a iiuid conducting duct comprisinga housing adapted to be mounted on said duct, electrical switch meansmounted in said housing, paddle rod means pivotally mounted at one endportions thereof in said housing and having its other end portionextending into said duct7 paddle means carried by said other end portionof said paddle rod means, said paddle means being movable by fluid ow insaid duct to effect movement of said paddle rod means, switch actuatormeans mounted on said one end portion of said paddle rod means andadjacent said electrical switch means for effecting actuation of thelatter upon a first predetermined amount of movement of said paddle rodmeans in one direction of uid fiow in said duct, and stop means mountedin said housing in position for engaging said switch actuator means toarrest movement of said paddle rod means upon movement of the same asecond predetermined amount beyond said first predetermined amount ofmovement in said one direction of fluid ow.

11. A ow switch for association with a fluid conducting duct comprisinga housing adapted to be mounted on said duct, electrical switch meansmounted in said housing, paddle rod means pivotally mounted at one endportion thereof in said housing and having its other end portionextending into said duct, paddle means carried by said other end portionof said paddle rod means, said paddle means being movable by fluid flowin said duct to effect movement of said paddle rod means, switchactuator means between said paddle rod means and said electrical switchmeans for effecting actuation of the latter upon a first predeterminedamount of movement of said paddle rod means in one direction of fluidflow in said duct, spring means mounted in said housing and engaging`said switch actuator means for resisting movement of said paddle rodmeans in said one direction of fluid fiow in said duct, and stop meansmounted in said housing in position for engaging said switch actuatormeans to arrest movement of said paddle rod means upon movement of thesame a second predetermined amount beyond said first predeterminedamount of movement in said one direction of fluid flow.

References Cited UNITED STATES PATENTS 2,038,111 4/1936 Hopkins 20G-81.92,211,553 9/1940 Bogue 200--81.9 3,126,463 3/ 1964 Kmiecik 20G- 81,93,147,620 9/ 1964 Stapler 73-228 BERNARD A. GILHEANY, Primary Examiner.

G. MAIER, H. BROOME, Assistant Examiners,

1. A FLOW SWITCH FOR ASSOCIATION WITH A FLUID CONDUCTING DUCT COMPRISINGA HOUSING ADAPTED TO BE MOUNTED ON SAID DUCT, ELECTRICAL SWITCH MEANSMOUNTED IN SAID HOUSING, PADDLE ROD MEANS PIVOTALLY MOUNTED AT ONE ENDTHEROF WITHIN SAID HOUSING AND WITH THE OTHER END OF SAID PADDLE RODMEANS EXTENDING INTO SAID DUCT, PADDLE MEANS CARRIED AT SAID OTHER ENDOF SAID PADDLE ROD MEANS, SAID PADDLE MEANS BEING MOVABLE BY FLUID FLOWIN SAID DUCT TO EFFECT MOVEMENT OF SAID PADDLE ROD MEANS, SAID PADDLEMEANS INCLUDING PIVOTABLE PADDLE COMPONENTS MOVABLE AROUND SAID OTHEREND OF SAID PADDLE ROD MEANS AND RELATIVE TO EACH OTHER FROM A FIRSTPOSITION BY PREDETERMINED FLOW OF AIR THROUGH SAID DUCT FOR DECREASINGTHE EFFECTIVE SURFACE AREA OF SAID PADDLE COMPONENTS OF SAID PADDLEMEANS EXPOSED TO FLUID FLOW IN SAID DUCT, SPRING MERANS IN ENGAGEMENTWITH SAID PIVOTABLE PADDLE COMPONENTS FOR NORMALLY BIASING SAID PADDLECOMPONENTS TOWARDS SAID FIRST POSITION, AND SWITCH ACTUATOR MEANSBETWEEN SAID ONE END OF SAID PADDLE ROD MEANS AND SAID ELECTRICAL SWITCHMEANS FOR OPENING AND CLOSING THE LATTER UPON PREDETERMINED MOVEMENT OFSAID PADDLE ROD MEANS.